(1). Field of the Invention
The present invention relates to substrate cleaning apparatus and substrate cleaning methods for cleaning surfaces of substrates such as semiconductor wafers, glass substrates for liquid crystal displays, glass substrates for photomasks and substrates for optical disks. In particular, a surface of such a substrate is cleaned while the substrate is spun, with cleaning devices such as cleaning brushes, high-pressure cleaning nozzles or ultrasonic cleaning nozzles.
(2). Description of the Related Art
A conventional substrate cleaning apparatus of this type, generally, includes one cleaning device supported by one support arm. The one cleaning device supported by the support arm is moved over a surface of a spinning substrate between the spin center and the outer periphery of the substrate to clean the entire surface of the substrate.
Where various cleaning devices such as a cleaning brush, a high-pressure cleaning nozzle and an ultrasonic cleaning nozzle are provided, each cleaning device is supported by a separate support arm. Each support arm (or cleaning device) is separately driven by an individual drive mechanism. A selected one of the cleaning devices is moved over a surface of a spinning substrate between the spin center and the outer periphery of the substrate to clean the entire surface of the substrate.
Conventional apparatus with such constructions have the following drawbacks.
Substrate size has been increasing in recent years, and in the case of semiconductor wafers, for example, 8-inch wafers are giving way to 300 mm wafers. Substrates have a larger turning radius (length from spin center to outer periphery) than before. Consequently, a longer time is now required for one cleaning device to move from the spin center to the outer periphery of a substrate. An extended cleaning time is becoming a matter of concern.
The spin velocity of a substrate is progressively higher toward the outer periphery thereof. When, for example, an entire surface of a substrate is cleaned with the same type of cleaning brushes and with the same conditions, regions adjacent the spin center of the substrate are vulnerable to damage, while peripheral regions may be cleaned insufficiently. Such a tendency is all the more outstanding with large substrates. Thus, in cleaning a surface of a large substrate with cleaning brushes, there has been a desire to clean central regions of the substrate with a soft cleaning brush such as a mohair brush in order to avoid damage, and peripheral regions with a hard cleaning brush such as a PVA brush in order to obtain an excellent cleaning result. Such a requirement may be satisfied with a conventional apparatus only by following a troublesome procedure. That is, the soft cleaning brush is attached to the support arm first to clean central regions of a large substrate. When the central regions have been cleaned, the support arm is moved to a retracted position once, and the soft brush is replaced with the hard one. Subsequently, peripheral regions of the large substrate are cleaned with the hard cleaning brush. This procedure poses a problem of low cleaning efficiency and extended cleaning time.
Where a cleaning process is performed by using various cleaning devices, a conventional apparatus cannot clean a surface of a substrate with the various cleaning devices at a time since the support arms supporting the respective cleaning devices would interfere with one another. Thus, the cleaning devices must be selected successively and driven individually for use. While one cleaning device is engaged in a cleaning operation, the other cleaning devices are kept on standby in retracted positions. All this results in low cleaning efficiency and extended cleaning time.
Moreover, the conventional apparatus has a complicated construction and is costly since a plurality of drive mechanisms are provided for the respective support arms supporting the different cleaning devices.